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Flashcards in Evolution Deck (40)
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Natural Selection

-"survival of the fittest"
-theory that certain characteristics or traits possessed by individuals within a species may help those individuals to have greater reproductive success and pass those trait to offspring
-mechanism for evolution, not the same thing as evolution
-the history of differential selection over time
-does not occur in populations that do not have any genetic diversity -- if entire population is homozygous at one loci then natural selection will not act on this gene


What are the 3 basic tenets that built the theory of natural selection?

-organisms produce offspring, few of which survive to reproductive
-chance variations that give an organism a slight survival advantage are considered favorable variations
-individuals with a greater preponderance of these favorable variations are more likely to survive to reproductive age and produce offspring; this level of reproductive success is termed fitness



-modern synthesis model of natural selection
-adds knowledge of genetic inheritance and changes in the gene pool to Darwin's original theory
-includes terms such as differential reproduction, inclusive fitness, and punctuated equilibrium


Differential Reproduction

-when mutation or recombination results in a change that is favorable to the organism's reproductive success, that change is more likely to pass on to the next generation (the opposite is true too)
-individuals with more viable offspring are selected for and individuals who produce less viable offspring are selected against


Because it is the gene pool that changes over time, it is _____ that evolve, not ____



Inclusive Fitness

-a measure of an organism's success in the population
-based on the number of offspring, success in supporting offspring, and the ability of the offspring to then support others
-promotes the idea that altruistic behavior can improve the fitness and success of a species as a whole (new concept for modern theories of natural selection and is not found in Darwin's theory)


Punctuated Equilibrium

-suggests that changes in some species occur in rapid bursts rather than evenly over time
-occurs when little evolution happens within a lineage of related lifeforms for long periods of time, followed by a massive explosion of evolutionary change


What are the 3 different modes of natural selection?

-stabilizing selection
-directional selection
-disruptive selection


Stabilizing Selection

-keeps phenotypes within a specific range by selecting against extremes
-intermediate phenotypes are more fit than extreme ones
-Ex. human birth weight is maintained within a narrow band by this type of selection


Directional Selection

-created by adapted pressure
-leads to the emergence and dominance of an extreme phenotype
-occurs when a new standard phenotype emerges as a result of differential survivorship
-Ex. heterogenous plate of bacteria that is treated with antibiotics and only those colonies that exhibit resistance to the antibiotic survive


Disruptive Selection

-two extreme phenotypes are selected over the norm
-extremes are more fit than those in the middle
-facilitated by polymorphisms
-Ex. finches on the Galapagos Islands only exhibited large or small beaks, none had a medium sized beak



naturally occurring differences in form between members of the same population, such as light and dark coloration in the same species of butterfly, or hair color


Adaptive Radiation

-describes the rapid rise of a number of different species from a common ancestor
-benefit of this is that it allows for various species to occupy different niches
-favored by environmental changes or isolation of small groups of the ancestral species
-this could occur (speciation) if one species was placed in several different environments



-a specific environment, (including habitat, available resources, and predators) for which a species can be specifically adapted



the largest group of organisms capable of breeding to form fertile offspring



-the formation of a new species
-this can occur due to barriers that prevent successful interbreeding within a species
-can also occur through evolution


What are the two ways reproductive isolation can occur?

-prezygotic mechanisms
-postzygotic mechanisms


Prezygotic Mechanisms

-prevent formation of a zygote completely
-examples: temporal isolation (breeding at different times), ecological isolation (living in different niches with the same territory), behavioral isolation (lack of attraction between members of the two species due to differences in pheromones, courtship displays, etc), reproductive isolation (incompatibility of reproductive anatomy), or gametic isolation (intercourse can occur but fertilization cannot)


Postzygotic Mechanisms

-allow for gamete fusion but yield either nonviable or sterile offspring
-examples: hybrid inviability (formation of a zygote that cannot develop to term), hybrid sterility (forming hybrid offspring that cannot reproduce), and hybrid breakdown (forming first-generation hybrid offspring that are viable and fertile but second-generation offspring are inviable or infertile)


What are the three patterns of evolution that can be seen when analyzing a species?

-divergent evolution
-parallel evolution
-convergent evolution


Divergent Evolution

-independent development of dissimilar characteristics in two or more lineages sharing a common ancestor
-Ex. seals and cats (or bats and horses) are both mammals in the order Carnivora yet they are very different in general appearance


Parallel Evolution

-the process whereby related species evolve in similar ways but through different mechanisms for a long period of time in response to analogous environmental selection pressures
-same lineage
-Ex. feeding structure of crustaceans -- came from a mutation in a pair of legs and turned them into mouth parts (lobsters, crabs, and shrimp have a common ancestor but are all different species that have similar mouth structures)


Convergent Evolution

-the independent development of similar characteristics in two or more lineages not sharing a recent common ancestor
-different lineage with similar environments
-Ex. fish and dolphins (or sharks and dolphins) have come to resemble one another physically although they belong to different classes of vertebrates



-ability to pass on genetic material through reproduction
-Ex. someone that is strong/healthy/long-lived that doesn't have any children is LESS FIT than someone who is weak/unhealthy/dies young but has 8 kids


Group Selection

-when natural selection acts on a group and NOT on an individual
-explains why altruism exists



-sacrifice the individual to benefit the group
-group should have the traits of the individual so that their traits are not lost


Evolutionary Success

-occurs when an allele can increases its frequency in the next generation
-gene has been passed down to next generation


Biological species must meet the following 3 conditions:

1. must be able to interbreed
2. must be able to produce viable, fertile offspring
3. must do all of the above naturally


Does the scenario below result in the creation of a species?

2 different plants interbreed and make fertile offspring, but one plant is pollinated by bees and the other is pollinated by birds

b/c breeding occurred through an unnatural way



genetic change in a population that is due to natural selection